A trench MOSFET with high speed switching

Abstract

A kind of trench MOSFET with high-speed switch. It relates to the field of semiconductor technology.The utility model trench MOSFET by adding source trench and supporting structure between adjacent gate trenches, build new current path.In reverse freewheeling, the current of traditional trench MOSFET needs to be all flowed through body diode, and in the structure, the source oxide layer in source trench is thinner, and the source and source region are short-circuited to form built-in MOS channel.When the device is in reverse working state, part of freewheeling current can flow through this built-in MOS channel, no longer completely rely on body diode, if the thickness of source oxide layer is appropriately reduced, even the whole freewheeling current can flow through MOS channel, completely not rely on body diode, so as to change the current flow path and distribution situation.This optimization of current channel can effectively reduce the storage and recombination time of carriers, and then improve the reverse recovery performance.

Description

Technical Field

[0001] This utility model relates to the field of semiconductor technology, and in particular to a trench MOSFET with high-speed switching. Background Technology

[0002] Trench MOSFETs are particularly attractive for switching circuits due to their sufficient voltage withstand capability, excellent conduction characteristics, ultra-high switching frequency, and parasitic body diode that can be used as a freewheeling diode. When trench MOSFET devices are used in switching circuits, the reverse recovery time of their body diode directly affects the overall circuit efficiency. Hard recovery of the trench MOSFET body diode can cause voltage overshoot and oscillations in the circuit. The fast and flexible body diode reduces switching losses, which is crucial for improving circuit efficiency and ensuring device reliability. The body diode is very useful as a buffer diode. However, its slow reverse recovery speed significantly increases power loss during switching, thus greatly limiting its application.

[0003] Several methods exist to improve the reverse recovery speed of the body diode. For low-voltage ranges (breakdown voltage below 50V), integrating a separate Schottky diode within the trench MOSFET chip avoids the parasitic body diode, which causes a large reverse leakage current. Compared to an external reverse parallel freewheeling diode, using the parasitic body diode inside the MOSFET for freewheeling or integrating the SBD inside the MOSFET device undoubtedly reduces circuit size, parasitic capacitance and inductance, and avoids additional parasitic effects. Furthermore, for MOSFETs with integrated fast recovery diode structures, since the SBD integrated within the cell uses the MOSFET device's drift layer and substrate, its manufacturing cost is lower than that of an externally integrated SBD. Compared to MOSFETs using a body diode for freewheeling, integrating the SBD... The reverse recovery characteristics of the BD structure are better, thus reducing device power consumption and avoiding the bipolar degradation phenomenon of the body diode. Furthermore, since temperature has little effect on the reverse recovery characteristics of Schottky diodes, the advantage of using an SBD for freewheeling is more pronounced at higher temperatures. However, the integrated SBD structure is not without its flaws. Studies have found that its surge reliability is not as strong as that of a body diode, making it less reliable than a MOSFET using a body diode for freewheeling. While the integrated SBD structure wastes less chip area compared to an external SBD structure, it still results in wasted chip area compared to a MOSFET using a body diode for freewheeling. Therefore, designing a trench MOSFET that reduces reverse recovery time and current is a crucial problem that needs to be solved in this case. Utility Model Content

[0004] To address the above problems, this invention provides a trench MOSFET that reduces the hole concentration in the drift region during forward conduction of the body diode, thereby improving reverse recovery performance.

[0005] The technical solution of this utility model is: A trench MOSFET with high-speed switching comprises, from bottom to top, a back metal layer, a sub layer, an epitaxial layer, a body region, a source region, an ILD dielectric layer, and a front metal layer connected in sequence. The epitaxial layer is provided with: A gate oxide layer is provided, which extends downward from the top surface of the source region into the epitaxial layer; Multiple gates are provided, each disposed within the gate oxide layer; A plurality of source oxide layers are provided, located between adjacent gate oxide layers near the end, extending downward from the top surface of the source region into the epitaxial layer; Multiple sources are provided, each disposed within the source oxide layer; The contact layer is provided in several parts, and the contact layer extends downward from the top surface of the ILD dielectric layer to the body region; the bottom of the contact layer is located between the gate oxide layer and the source oxide layer or between the gate oxide layer and the gate oxide layer.

[0006] Specifically, the contact layer has a trapezoidal structure that is wider at the top and narrower at the bottom.

[0007] Specifically, the thickness of the gate oxide layer is 200 Å to 500 Å.

[0008] Specifically, the thickness of the source oxide layer is 30 Å to 70 Å.

[0009] Specifically, the thickness of the source oxide layer is less than the thickness of the gate oxide layer.

[0010] Specifically, the epitaxial layer is disposed on the sub layer.

[0011] Specifically, the sub-layer is an N+ layer or a P+ layer.

[0012] Specifically, the bottom of the gate oxide layer and the bottom of the source oxide layer are respectively arc-shaped structures.

[0013] This novel trench MOSFET constructs a new current path by adding a source trench and supporting structures between adjacent gate trenches. In reverse freewheeling mode, the current in a traditional trench MOSFET must flow entirely through the body diode. However, in this structure, the source oxide layer within the source trench is thinner, and the source and source regions are shorted to form a built-in MOS channel. When the device is in reverse operation, a portion of the freewheeling current can flow through this built-in MOS channel, no longer entirely dependent on the body diode. If the source oxide layer thickness is appropriately reduced, even all freewheeling current can flow through the MOS channel, completely independent of the body diode, thus changing the current flow path and distribution. This optimization of the current path effectively reduces carrier storage and recombination time, thereby improving reverse recovery performance. Attached Figure Description

[0014] Figure 1 This diagram illustrates the current flow direction when the gate channel is open and a positive voltage is applied to the source and drain. Figure 2 This diagram illustrates the current flow when the gate channel is closed, the source channel is open, and a negative voltage is applied to the source and drain. Figure 3 This indicates the formation of a gate trench structure; Figure 4 This indicates the formation of a source trench structure; Figure 5 This indicates the formation of the ILD dielectric layer and vias; Figure 6 This indicates the formation of the front and back metal sections; In the diagram, 1 is the sub-layer, 2 is the epitaxial layer, 3 is the gate trench, 4 is the gate oxide layer, 5 is the gate, 6 is the body region, 7 is the source region, 8 is the source trench, 9 is the source oxide layer, 10 is the source, 11 is the ILD dielectric layer, 12 is the contact layer, 13 is the front metal layer, and 14 is the back metal layer. Detailed Implementation

[0015] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model.

[0016] In the description of this utility model, it should be understood that the terms "upper," "lower," "left," "right," "vertical," "horizontal," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. In the description of this utility model, unless otherwise stated, "a plurality of" means two or more.

[0017] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0018] In conventional structures, the gate electrode controls two forward-conducting channels. However, the VDMOSFET structure with an integrated channel diode requires a design that enables two turn-on voltages for the two channels: the gate channel turns on when it is forward-conducting, and the source control channel turns on when it is reverse-conducting and freewheeling. The threshold voltage is affected by factors such as the thickness of the gate oxide layer and the carrier concentration in the channel region. By thinning the oxide layer on both sides of the source trench, the design of two turn-on voltages for the two channels in the trench MOSFET structure with an integrated channel diode can be achieved.

[0019] When the gate voltage of a trench MOSFET with a built-in channel diode is greater than the gate-channel threshold voltage, a forward voltage is applied across the drain and source terminals. Electrons pass through the gate-controlled channel, through the drift region and substrate, and reach the drain terminal. Figure 1 With no voltage applied to the gate and a reverse voltage applied across the drain and source terminals, the source control channel and body diode share the freewheeling current. (See...) Figure 2 .

[0020] The reverse recovery process of the body diode completely extracts or neutralizes the minority carrier holes injected into the drift region from the P-type region when the body diode is turned on. This changes or increases the current path during reverse freewheeling, so that the current that originally passed entirely through the body diode is now shared by the source-controlled channel and the body diode or entirely by the source-controlled channel. This reduces the hole concentration stored in the drift region, reduces the reverse recovery time and reverse recovery charge, and improves the reverse recovery performance.

[0021] This article only uses Trench MOS as an example. Any product with a body diode, long reverse recovery time, and large reverse recovery current can be realized through this utility model.

[0022] A trench MOSFET with high-speed switching includes, from bottom to top, a back metal layer 14, a sub layer 1, an epitaxial layer 2, a body region 6, a source region 7, an ILD dielectric layer 11, and a front metal layer 13 connected in sequence. The epitaxial layer 2 is provided with: The gate oxide layer 4 has several U-shaped cross-sections and extends downward from the top surface of the source region 7 into the epitaxial layer 2. Multiple gates (5) are provided and are respectively disposed within the gate oxide layer 4; The source oxide layer 9 has several U-shaped cross-sections and is located between adjacent gate oxide layers 4 near the ends, extending downward from the top surface of the source region 7 into the epitaxial layer 2; the bottom of the source oxide layer 9 is not lower than the bottom of the gate oxide layer 4. Multiple source electrodes 10 are provided and are respectively disposed within the source electrode oxide layer 9; The contact layer 12 is provided in a plurality of manner, the contact layer 12 extending downward from the top surface of the ILD dielectric layer 11 to the body region 6, and the bottom is located between the gate oxide layer 4 and the source oxide layer 9 or between the gate oxide layer 4 and the gate oxide layer 9.

[0023] The contact layer 12 has a structure that is wider at the top and narrower at the bottom.

[0024] The bottom of the gate oxide layer 4 and the bottom of the source oxide layer 9 are located below the body region 6, respectively. The bottom of the gate oxide layer 4 and the bottom of the source oxide layer 9 are both arc-shaped structures.

[0025] In this case, the gate oxide layer 4 extends downward to a depth of 200 Å to 800 Å; the source oxide layer 9 extends downward to a depth of 30 Å to 100 Å.

[0026] like Figure 1 The diagram shows the current flow direction when the MOSFET is forward-biased. When the gate voltage is greater than the threshold voltage, a forward voltage is applied across the drain and source terminals (i.e., +VD is applied to the drain and the source is grounded). Electrons enter the epitaxial layer from the source through the gate channel and move along the epitaxial layer to the bottom drain. The arrows represent the direction of electron charge flow.

[0027] like Figure 2 The diagram shows the current flow of a MOSFET during reverse conduction. At this time, the gate voltage is zero, and a reverse voltage is applied across the drain and source terminals (i.e., -VD is applied to the drain and the source is grounded). During the period from forward conduction to sudden turn-off and reverse conduction of the MOSFET, the minority carrier holes stored in the epitaxial layer during forward conduction reach the source through the open source channel and the body diode, and continue to flow together. By reducing the thickness of the source oxide layer, the reverse current can be made to flow entirely through the source channel without passing through the body diode, thereby greatly reducing the reverse recovery charge and reverse recovery time, and reducing the reverse conduction loss. This invention introduces a source trench 8, changing the previous situation where the current was solely carried over by the body diode. Instead, the source channel and the body diode work together to carry over the current in reverse, reducing the hole concentration in the drift region when the body diode of the trench MOSFET is forward-biased, improving the reverse recovery performance, and reducing the reverse recovery time and current of the trench MOSFET.

[0028] A method for fabricating a trench MOSFET with high-speed switching includes the following steps: Step 1: Multiple gate trenches 3 are formed on the epitaxial layer 2 by etching using a gate mask; Step 2: Oxidation is performed in the gate trench 3 to form the gate oxide layer 4; Specifically, the gate oxide layer 4 has a thickness of 200 Å to 800 Å and a U-shaped cross-section; Step 3: Deposit the first polysilicon on the gate oxide layer 4 in the gate trench 3, and etch to form the gate 5; Step 4: Perform P or N type ion implantation on epitaxial layer 2 to form body region 6; the doping concentration is 2E12~9E12; Step 5: Perform N or P type ion implantation on body region 6 to form source region 7, see... Figure 3 As shown; the doping concentration is 2E15~8E15; Step six: Using a source mask, a source trench 8 is etched between adjacent gate trenches 3 near the end of the body region 6 to form a source trench 8. A source oxide layer 9 is then formed within the source trench 8 by oxidation. A second polysilicon layer is deposited within the source oxide layer 9 and shorted to the source region 7 to form a source 10. Figure 4 As shown; Specifically, the source oxide layer 9 has a thickness of 30 Å to 100 Å and a U-shaped cross-section; The thickness of the source oxide layer 9 in the source trench 8 is less than the thickness of the gate oxide layer 4. The separated source forms a built-in MOS channel, changing the original current path that all current needs to pass through the body diode, thus improving the reverse recovery time and reverse recovery charge of conventional trench MOSFETs. The gate oxide layer 4 (thickness 200Å~800Å) is the core insulating layer of the MOSFET. Its main function is to isolate the gate 5 from the channel and withstand the voltage difference (i.e., gate voltage) between the gate 5 and the source / drain. A thicker oxide layer can improve the breakdown voltage of the gate 5, ensure the stability and reliability of gate 5 control, and prevent leakage or breakdown between the gate 5 and the channel.

[0029] The source oxide layer 9 (thickness 30Å~100Å) within the source trench 8 serves to construct the "built-in MOS channel". The thinner oxide layer reduces the threshold voltage between the source 10 and the channel, making it easier to form a conductive channel during reverse freewheeling: when the device is in reverse operation, the thinner oxide layer allows an additional current path to be opened at a lower voltage, allowing some of the freewheeling current to flow through this channel instead of relying entirely on the body diode.

[0030] The gate oxide layer 4 needs to ensure the reliability of gate 5 control (relatively thick), and the source oxide layer 9 needs to ensure the easy opening of the channel during reverse freewheeling (relatively thin). With this structure, normal gate control can be maintained when the MOSFET is forward conducting, and efficient current shunting can be achieved during reverse freewheeling, thereby improving the reverse recovery characteristics.

[0031] Step 7: Deposit an ILD dielectric layer 11 on the epitaxial layer 2; Step 8: A hole with a wide top and narrow bottom structure is formed on the ILD dielectric layer 11 using a dry etching process. Tungsten is then deposited using PVD and etched back to form contact holes 12, as shown below. Figure 5 As shown; Step nine, as Figure 6 As shown, a front metal layer is prepared on the front side of the device (13); after thinning on the back side, a back metal layer is prepared (14).

[0032] This invention forms a built-in MOS channel by separating the trench source, changing the current path that originally relied entirely on the body diode for freewheeling. This significantly shortens the reverse recovery time, reduces the reverse recovery charge, lowers device power consumption, and solves the problem of poor reverse recovery performance in conventional trench MOSFETs. Simultaneously, it reduces the reliance on the body diode, thereby lowering the probability of body diode bipolar degradation and improving device stability and lifespan.

[0033] Compared to structures integrating a Schottky diode (SBD) outside the cell, this invention does not occupy excessive chip area, avoiding significant area waste. Furthermore, by utilizing existing process steps, it does not significantly increase manufacturing costs. It achieves similar advantages to SBDs—low temperature sensitivity—without relying on a Schottky diode (SBD) for freewheeling, maintaining good reverse freewheeling performance even at higher temperatures. It avoids the problem of poor surge reliability inherent in integrated SBD structures, offering superior reliability compared to integrated SBD structures and approaching the reliability of MOSFETs using body diodes for freewheeling.

[0034] Regarding the information disclosed in this case, the following points need to be clarified: (1) The accompanying drawings of the embodiments disclosed in this case only involve the structures involved in the embodiments disclosed in this case. Other structures can refer to the general design. (2) Where there is no conflict, the embodiments and features disclosed in this case can be combined with each other to obtain new embodiments; The above are merely specific embodiments disclosed in this case, but the scope of protection of this disclosure is not limited thereto. The scope of protection disclosed in this case shall be determined by the scope of protection of the claims.

Claims

1. A trench MOSFET with high-speed switching, characterized in that, From bottom to top, it includes a back metal layer (14), a sub layer (1), an epitaxial layer (2), a body region (6), a source region (7), an ILD dielectric layer (11), and a front metal layer (13) connected in sequence. The epitaxial layer (2) is provided with: A gate oxide layer (4) is provided, which extends downward from the top surface of the source region (7) into the epitaxial layer (2); Multiple gates (5) are provided and are respectively disposed within the gate oxide layer (4); A source oxide layer (9) is provided in several places, located between adjacent gate oxide layers (4) near the end, extending downward from the top surface of the source region (7) into the epitaxial layer (2); Multiple source electrodes (10) are provided and are respectively disposed within the source electrode oxide layer (9); A plurality of contact layers (12) are provided, the contact layers (12) extending downward from the top surface of the ILD dielectric layer (11) to the body region (6); the bottom of the contact layers (12) is located between the gate oxide layer (4) and the source oxide layer (9) or between the gate oxide layer (4) and the gate oxide layer (4).

2. A trench MOSFET with high-speed switching according to claim 1, characterized in that, The contact layer (12) has a trapezoidal structure that is wider at the top and narrower at the bottom.

3. A trench MOSFET with high-speed switching according to claim 1, characterized in that, The thickness of the gate oxide layer (4) is 200 Å to 500 Å.

4. A trench MOSFET with high-speed switching according to claim 1, characterized in that, The thickness of the source oxide layer (9) is 30 Å to 70 Å.

5. A trench MOSFET with high-speed switching according to claim 1 or 4, characterized in that, The thickness of the source oxide layer (9) is less than the thickness of the gate oxide layer (4).

6. A trench MOSFET with high-speed switching according to claim 1, characterized in that, The epitaxial layer (2) is disposed on the sub-layer (1).

7. A trench MOSFET with high-speed switching according to claim 1, characterized in that, The sub-layer (1) is an N+ layer or a P+ layer.

8. A trench MOSFET with high-speed switching according to claim 1, characterized in that, The bottom of the gate oxide layer (4) and the bottom of the source oxide layer (9) are respectively arc-shaped.

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